1. Field of the Invention
The present invention relates to a floppy disk driver for loading a floppy disk for analog recording of signals, such as a floppy disk driver for analog recording of image signal, and is more particularly concerned with a floppy disk driver incorporating protective rotation control apparatus for avoiding disk and/or driver damage due, for example, to shape or mounting defects of the disk.
2. Related Background Art
In a floppy disk for analog recording, unevenness in rotation directly affects the reproduced signal. Consequently a higher precision in rotation is required in the analog recording than in the digital recording.
In the following description, a video floppy disk for handling image signals will be considered as an example of analog recording.
For controlling the rotation of a diskdriving motor, there have been known a phase control method and a speed control method. In the phase control method, the rotation is so controlled that the phase of a rotation phase signal, generated in every turn of the motor, coincides with that of a reference clock signal. In the speed control method, the rotation is controlled by detecting the rotating speed of the motor. The phase control method is superior in precision to the speed control method, but requires a longer time from the start to the lock-in state, as the increase of revolution at the start of motor is slower.
For avoiding the drawbacks of these methods, there has been proposed, for example in the U.S. Pat. No. 4,658,191, an apparatus provided with means for detecting that the difference between the phase of the reference clock signal and the rotating phase of the motor is within a predetermined range, and the above-mentioned drawbacks are avoided by switching the speed control method and the phase control method according to the phase difference.
If fluctuation exists, at the signal recording or reproduction, in the rotation of the video floppy disk (hereinafter simply called disk) for analog recording of image signal, the recorded or reproduced image becomes distorted and is deteriorated in quality. For preventing such phenomenon, there may be provided means for detecting the fluctuation in rotation, thereby interrupting the signal recording or reproduction. For detecting such fluctuation in rotation there has been proposed, for example in the Japanese Laid-open Patent Sho 59-178364, a device which generates plural pulses in every turn of the motor, inspects whether the intervals of said plural pulses are within a predetermined range, and identifies an abnormality in rotation if said interval is outside said range. The recording operation, for example in an electronic still camera, with a floppy disk driver equipped with a rotation control device and a device for detecting the fluctuation in rotation is conducted in the following manner. After the start of power supply, the disk reaches a constant revolution (called locked-in state) by said rotation control device. Then the image of an object is taken with a solid-state image sensor, and the output signal therefrom is processed by a signal processing circuit The output of said circuit is recorded on the disk, after the absence of fluctuation in rotation is confirmed by said fluctuation detecting device.
The conventional floppy disk drive is, at least in principle, kept free from fluctuation in rotation by a servo mechanism of said rotation control device, once the disk reaches the constant rotation state by said rotation control device Consequently the abovementioned fluctuation detecting device has been omitted in conventional floppy disk drives. However certain external perturbations not absorbable by said servo mechanism can exist particularly in drives used in the hand-held state, such as those in the electronic still camera. The above-mentioned fluctuation detecting device is therefore being utilized as a measure for such external perturbation.
As an example of a video floppy disk, there is known the standardized 2-inch video floppy disk. When a great number of such 2-inch video floppy disks are mass produced, there may appear defective ones of which shape, particularly the shape of the hub, does not meet standardized specifications. Such defective video floppy disk may touch a part of the disk drive during a turn, thus causing a fluctuation in torque in a position of the disk. Also such torque fluctuation in a certain position may appear even with a non-defective video floppy disk, in case the disk is inclined by a chucking error or by the presence of dust particles. FIG. 1 illustrates the cause of such torque fluctuation in simplified and exaggerated manner. In FIG. 1, (.alpha.) indicates the position of a shape defect or dust, and a disk 3 mounted on a loader L is thus inclined and contacts the most prominent part (.beta.) of an opposed machine part of the disk drive (so designated), thus causing fluctuation in torque applied by a disk drive motor 1.
If there is significant contact between the video floppy disk and the disk driver, the fluctuation in torque becomes larger and the rotation cannot reach the locked-in state at the start of the motor. There is already employed, therefore, a method of interrupting the operation if the disk does not reach the locked-in state within a predetermined time after the start of the motor. However, if said contact between the video floppy disk and the disk driver is not significant, the disk can reach the locked-in state. In such case the fluctuation in rotation can still occur by the contact between the video floppy disk and the disk driver even after said locked-in state is reached, but such contact cannot be detected since said fluctuation in rotation is absorbed within a short time by the aforementioned rotation control device. In the conventional electronic still cameras, as explained before, the recording or reproducing operation is conducted when the absence of fluctuation in rotation is confirmed by the fluctuation detecting device after the rotation of the video floppy disk reaches the locked-in state, and such recording or reproducing operation cannot be interrupted once it is started, even if fluctuation in rotation occurs in the course. Since the aforementioned fluctuation in rotation, resulting from the contact between the video floppy disk and the disk driver, is periodical, such recording or reproducing operation is actually conducted with periodic fluctuation in rotation. Also, the repeated contact between the video floppy disk and the disk driver will eventually abrade the video floppy disk or the disk driver, thus causing damage therein. These phenomena are not limited to video floppy disks but appear in any analog video floppy disks and the corresponding disk drivers. For the purpose of simplicity, a driver for video floppy disk will be described in the following.